Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to wireless communications, including mobile wireless communications over cellular telephone systems. The invention further relates to real-time (e.g., voice, multimedia, etc.) communications across multiple networks. More particularly, the invention concerns a method for optimizing real-time communications routed from one mobile wireless unit to another, or from a mobile wireless unit to a wireline unit, across plural interconnected networks, and especially between a circuit-oriented voice network and a data network implementing connectionless network layer datagram routing.
2. Description of the Prior Art
Considerable attention has been directed toward the implementation of real-time communication across computer data networks, and particularly the ability to route voice traffic to and from the Public Switched Telephone Network (PSTN). There has been related interest in using so-called Voice over IP (VoIP) solutions to facilitate voice communication between originating and terminating PSTN end points, using the Internet for long haul routing while substantially bypassing the PSTN. Similar proposals have been made for routing voice traffic as ATM packets over Asynchronous Transfer Mode (ATM) networks (VoATM).
Traditionally, voice calls are transported entirely over the end-to-end, circuit-based PSTN. For PSTN bypassing applications, it has been proposed that PCM voice traffic be processed into IP (or ATM) packets, transported over the Internet (or ATM network), and then processed back to PCM voice. To facilitate such call routing, the originating and terminating End Office (EO) switches can be connected to PSTN/IP (or PSTN/ATM) gateways that reside as hosts on the IP (or ATM) network. Based on the called number or other signaling indicator, the EO switches route certain calls through the IP (or ATM) gateways instead of the PSTN.
It would be desirable if the foregoing VoIP topology could be used by mobile wireless telephone subscribers as well as wireline users. For example, a wireless gateway interconnecting a Mobile Switching Center (MSC) and an IP or ATM network would enable wireless traffic to be routed outside of the PSTN. However, inefficiencies would be introduced due to the delays inherent in wireless environments. These delays are particularly acute in digital wireless systems where voice encoder/decoders (vocoders) in the mobile radio units are used to digitize (and compress) analog voice signals of fixed duration (e.g., 20 ms). The sampled input is converted into corresponding digital wireless frames for air interface transmission according to a wireless-specific vocoding standard, such as one of the algorithms for TDMA (Time Division Multiple Access), CDMA (Code Division Multiple Access) or GSM (Global System for Mobile Communications) mobile networks. A receiving-end vocoder in the MSC (or in a Base Station (BS)) decompresses the digital wireless frames and converts the information into digital wireline traffic in accordance with an uncompressed encoding format such as PCM (Pulse Code Modulation). If the PCM traffic is routed to an originating PSTN/IP gateway for transmission across the Internet, vocoding would typically again be performed to compress the information for improved IP transport efficiency. The terminating PSTN/IP gateway would then reconvert the compressed information into uncompressed PCM traffic to be sent to the terminating EO. In all, there would be four vocoding steps for every transmission between a mobile wireless unit and a remote wireline unit. If the remote unit is another mobile wireless unit, there would be six vocoding operations performed. The delays produced by these vocoding operations may be unacceptable to users.
Accordingly, there is a need in a mobile wireless communication system for a method of optimizing voice or other real-time wireless communications routed across plural interconnected networks without the above-described inefficiencies. What is required is a communication method that eliminates the overhead associated with repeated encoding/decoding (e.g., vocoding) steps so as to improve call throughput efficiency and minimize transmission delays.
A method for optimizing mobile wireless communication across plural interconnected networks provides a novel solution to the foregoing problem. In accordance with the inventive method, a telecommunication system routes real-time information traffic from an originating digital radio unit served by an originating network to a terminating unit (which could also be a digital radio) served by a terminating network, via an intermediate network that interconnects the originating and terminating networks. The originating and terminating networks could be one and the same, or they could be independent networks. The intermediate network could be any suitable telecommunication network. The originating digital radio unit communicates with the originating network via an originating node. This originating node, in turn, communicates with an originating-end interface node in the intermediate network. These nodes would typically be situated remotely from each other, but could also be co-located. The terminating unit communicates with the terminating network via a terminating node. This terminating node, in turn, communicates with a terminating-end interface node in the intermediate network. Again, these nodes could be co-located together or situated remotely from each other.
The originating digital radio unit has an encoder/decoder (e.g., a vocoder) for generating digital wireless frames from information input to the radio unit. The originating node of the originating network contains an encoder/decoder for converting the digital wireless frames into digital wireline, e.g., PCM, traffic. The originating-end interface node of the intermediate network contains an encoder/decoder for converting the digital wireline traffic received from the originating node of the originating network into compressed digital wireline traffic. Optimization of communications routed between the originating radio unit and the terminating unit is achieved by routing the former unit""s digital wireless frames without further encoding or decoding through at least the originating node of the originating network, and preferably through both the originating node of the originating network and the originating-end interface node of the intermediate network, such that the rate of information traffic throughput is maximized.
In preferred embodiments of the invention, the originating and terminating networks are part of a single telephone network, such as the PSTN, and the intermediate network is a computer data network that routes information using a network layer datagram protocol such as IP, a link layer protocol such as ATM, or both. The originating node in the originating network is preferably a cellular network MSC or MSC/BS combination (if vocoding is performed at the BS). The terminating node in the terminating network is preferably a terminating EO serving a terminating wireline unit, or a cellular network MSC or MSC/BS combination serving a terminating wireless unit. The originating-end and terminating-end interface nodes of the intermediate network are preferably network gateway platforms implementing a multimedia protocol such as H.323 or any other suitable standard. The originating MSC and the terminating EO or MSC would typically connect thereto via T1 or E1 trunks carrying time division-multiplexed digital wireline traffic.
When the digital wireless frames transmitted by the originating digital radio unit are received at the originating BS or MSC, the usual wireless-specific conversion into digital wireline traffic is not performed. Instead, the digital wireless frames are routed to the originating network gateway. The usual compression conversion performed at the originating network gateway is also eliminated and the digital wireless frames are encapsulated into network datagram packets for routing to the terminating network gateway. It is at the latter gateway that the second wireless-specific encoding/decoding operation is preferably performed to convert the digital wireless frames into digital wireline frames. These digital wireline frames are routed onto the trunk extending between the terminating network gateway and the terminating EO or MSC. At the terminating EO or MSC, the digital wireline frames can be further processed depending on the nature of the terminating unit, (i.e., whether it is a wireless or wireline, digital or analog device).